Helically wound reinforcing components for flexible tubular conduits

ABSTRACT

This invention relates to flexible tubular conduits or pipes particularly in situations where the conduits need to withstand relatively high pressures. In such cases, the conduits are reinforced by helically wound armor which is compliant in flexure, and profiled to allow each subsequent turn to interlock with the previous turn. The invention provides a locking mechanism ( 8, 9 ) located in the axial direction of the tubular conduit comprising one or more projections ( 8 ) on one or both radial sides and a corresponding number of sockets ( 9 ) on the opposing radial sides, such that the projections ( 8 ) of one turn of the winding ( 10 ) engaging in the sockets ( 9 ) of the next turn of the winding ( 10 ), each projection ( 8 ) having an enlarged head portion ( 11 ) connected to a body by a narrow neck portion ( 12 ), and each socket having a corresponding shape to hold the projection captive in the socket, the sockets ( 8 ) and projections ( 9 ) having dimensions to allow a limited relative rotation between the adjacent turns of the winding and to resist separation, closing, and relative radial movement of the respective turns.

This invention relates to flexible tubular conduits or pipes,particularly in situations where the conduit needs to withstandrelatively high pressures (typically greater than 50×10⁵ N/m²). In suchcases, the conduits are reinforced by helically wound armour which iscompliant in flexure, and profiled to allow each subsequent turn tointerlock with the previous turn. Generally, the armour is formed fromsteel or composite strip.

An example of this type of tubular conduit is un-bonded flexible pipe,used in the recovery of offshore hydrocarbon deposits. FIG. 1 is aschematic illustration of several arrangements of such pipe in use invarious dynamic configurations, in which the pipe is being used toconnect a sub-sea well to a floating platform. These are the “freehanging” (A), “Steep S” (B), “Lazy S” (C), “Steep Wave” (D), and “LazyWave” (E) configurations. Flexible pipes may also be used in staticapplications (not shown) to connect sub-sea wells to, for example, amanifold, or to tie wells which are several kilometers distant to anexisting sub-sea infrastructure. There are of course other applicationsin addition to the offshore applications mentioned here.

An illustration of a flexible conduit, typically used in offshoreapplications, is shown in FIG. 2. It can be seen that successive layersare used, each layer designed to perform a particular function. Theinnermost layer 1 is usually an interlocking carcass that resistscollapse due to external pressure. This is manufactured from a flatstrip which is bent into an appropriate shape. The next layer is aninner polymer barrier 2, which is a fluid retention layer, and seals thewell fluids inside the pipe. This is surrounded by an interlockedpressure armour 3 which is designed to resist internal pressure loading.Supported by an (optional) flat profiled spiral armour 4, theinterlocked pressure armour 3 has a shallow helical angle and acts inthe manner of hoops around a barrel. A variety of pressure armour 3profiles exist in the public domain for use in such offshoreapplications, some of which are shown in FIG. 3.

The function fulfilled by the layers 1-4 are the subjects of theinvention described herein. The remaining outer layers 5, 6, and 7, ofthe pipe shown in FIG. 2, are tensile armour wires designed to supportaxial load, and polymer layers used to prevent wear, or water ingress inthe case of the outermost layer 7.

Flexible pipe manufacture is carried out using a sequence of continuousprocesses. First, the carcass layer 1 is manufactured for the entirepipe length, which may be as much as several kilometers long. Then, thepolymer sealing layer(s) 2 is/are extruded onto the carcass layer 1 andcooled. A polymer tape may also be used in the application of thislayer. The pipe is then fed into a winding machine, which is used toapply the armour layer(s) 3 and 4. This sequence of alternate polymerextrusions (and/or tape laying) and armour winding is continued untilthe fill pipe structure is built.

The profiled strips making up the armour layers 3 and 4, are currentlymanufactured using a wire-drawing process. Strips are produced with across-sectional profile consisting of a sequence of lines and arcs. Theouter armour layer 4 is generally rectangular in cross section. Incontrast, there are a number of, albeit limited, profiles currentlyavailable for the inner pressure armour 3, some of which are shown inFIG. 3. These are the “Carcass” (A), “Zee” (B), “Tee” (C) and “Cee” (D)profiles, and have been the subject of several published patentapplications including W092/00481, W092/02751, and W091/00467. Of these,the Z˜shape (B) and the C˜shape (D) are most commonly used in currentoffshore flexible pipes.

For all such profiles in the public domain, the cross-sectional areadistribution is currently designed to make the normal second moment ofarea substantially more than the second moment of area in the bi-normaldirection. Typically, the bi-normal second moment of area is currentlyless than 20% of the normal second moment of area. The terms “normal”and bi-normal” refer to axes particular to the geometry of a helix, andare described in FIG. 4. In this figure, where OX₃ is the pipe axis andOX₁ and OX₂ are the radial directions, A is the normal (radial) axis, Bis the bi-normal (axial) axis and C is the tangential axis of the helix;α° is the helical angle. The application of this helical geometry to aC-shape profile is shown in FIG. 5. The bi-normal second moment of area,I_(B), is taken about axis B, and the normal second moment of area,I_(N), is taken about axis N. Profiles with such area distributions havelimited stress capacity in the radial directions.

In addition to resisting the pressure loading, the structural integrityof the conduit or pipe is maintained by interlocking subsequent turns ofpressure armour, for example in the manner shown in FIG. 3. Thismechanism must be applicable to a continuous assembly process duringpipe manufacture and, in use, must allow some axial movement andflexural rotation of the structure whilst, at the same time, preventingthe existence of excessive gaps in the pressure armour 3.

For the pressure armour layer 3, the primary mode of loading is theinternal pressure of the fluids flowing, or contained within, the pipe.A second load is applied to the structure in flexure (seen locally astension or compression in the layer), while axial tension and externalpressure are additional loads. It has been established by the inventorsthat up to 90% of the internal pressure load is dissipated in thispressure armour layer 3. The stress expected in the layer, as a resultof the functional loading, may be calculated and maximum limits set fora safe design. For flexible pipe in offshore applications, these stresslimits are currently dictated by the American Petroleum Institute (API)specification 17J. A substantial reduction in the stresses developed inthe pressure armour is the benchmark test that has been used to assessthe improvements in the pressure armour layer(s) of this invention. Asimilar criterion is used to judge the carcass layer 1, which resistsexternal pressure and prevents collapse of the pipe due to hydrostaticpressure.

The existing profiles, some of which are shown in FIG. 3, have reachedtheir technical hard point, or limit of utility. The pressure capabilityof a given thickness of these armour profiles, for the range ofmaterials typically used, is not sufficient to meet the intense demandsof many applications, such as the high temperature and increasingly highpressure offshore environments. Furthermore, concerns about fretting andfatigue means that the connection mechanisms currently employed by theseprofiles needs to be revised. This is because the point of contactbetween the turns is also the location of maximum stress in all loading;flexure, tension, and pressure. Furthermore, the existing profiles havesubstantial gaps (of the order 1-3 mm) between subsequent turns, whichare undesirable. To address these concerns, and to enable higherpressure ratings and/or deeper water capability, as well as possibleweight reduction benefits, several original profiled components havebeen developed for such tubular conduits.

Accordingly, the present invention provides a flexible tubular conduithaving a reinforced wall structure comprising at least one componentwound helically, the component comprising a body having one or moreprojections on one or both radial sides and a corresponding number ofsockets on the opposing radial sides, the projections of one turn of thewinding engaging in the sockets of the next turn of the winding, eachprojection having an enlarged head portion connected to the body by anarrow neck portion, and each socket having an enlarged portion toreceive the head portion of the corresponding projection and a narrowopening on which the neck engages to hold the projection captive in thesocket, the sockets and projections having dimensions to allow a limitedrelative rotation between the adjacent turns of the winding and toresist separation, closing, and relative radial movement of therespective turns.

The capacity of the component to support high stress situations ispartially dependent upon the relative area distributions of the numerouselements which make up the component, and increases as the relative areadefined by the projection is reduced. Therefore, in one embodiment ofthe invention, the cross sectional area of each projection issubstantially less than the cross sectional area of the component bodyexcluding the area of each projection. Preferably, the cross sectionalarea of each projection should be less than 50% of the cross sectionalarea of the component body excluding the area of each projection. Morepreferably, the cross sectional area of each projection is less than 40%of the cross sectional area of the component excluding the area of eachprojection. More preferably still, the cross sectional area of eachprojection is less than 30% of the cross sectional area of the componentbody excluding the area of each projection. Advantageously, the crosssectional area of each projection is preferably less than 20% of thecross sectional area of the component body excluding the area of eachprojection. Preferably, the cross sectional area of each projection isless than 10% of the cross sectional area of the component bodyexcluding the area of each projection.

Excess reinforcement within the component only adds weight to thetubular conduit, and does not provide any substantial increase instructural capacity when resisting the action of external pressure.Accordingly, the helically wound components would preferably compriseone or more fully enclosed internal cavities, separate to the socketrecesses.

By definition, a given force applied over a small area produces a higherpressure than the same force applied over a larger area. Advantageously,in another embodiment of the invention, the axial compression forcesbetween adjacent turns of the winding are substantially transmittedthrough contact between radial sides of the component body, and notthrough contact between projection and socket. Accordingly, the lengthof the projection measured from its root, on one radial side of thebody, may be substantially shorter than the depth of the correspondingsocket, measured from the opposing radial side of the body.

In another embodiment of the invention, the socket recess is configuredto resist radial opening of the recess. Specifically, the socket recessmay be reinforced by sufficient surrounding material to resist radialopening of the recess.

In a further embodiment of the invention, the tubular conduit isconfigured to operate at pressures of greater than 5×10⁵ N/m².Preferably, the tubular conduit is configured to operate at pressures ofgreater than 10×10⁵ N/m². More preferably, the tubular conduit isconfigured to operate at pressures of greater than 100×10⁵ N/m². Morepreferably still, the tubular conduit is configured to operate atpressures of greater than 200×10⁵ N/m².

In a further embodiment still, at least one projection and thecorresponding socket of the component are located at a position closerto the radially outer surface of the component than the radially innersurface. Thus, these projections would be located at a position wherethey would be subject to a reduced stress.

In another embodiment, the component is characterised by a cross-sectionwhose second moment of area about the bi-normal (axial) direction is atleast 20%,the second moment of area of the cross section about thenormal (radial) direction. Specifically, the component is characterisedby a cross section whose second moment of area about the bi-normal(axial) direction is at least two thirds of, if not greater than, thesecond moment of area of the cross section about the normal (radial)direction. Thus, the pressure capability of the component, and thus thetubular conduit, to resist radial forces is increased.

Preferably, the narrow opening of the socket is defined by opposingcurved walls, and the projection has a corresponding curved neck toengage with the curved walls and thus allows relative rotation whilstavoiding singular point contact.

Conveniently, the head portion of the projection of the component has asubstantially circular profile in cross-section, and the socket has acorresponding circular profile to engage with the circular head portionand to allow relative rotation between the projection and the socket,with the avoidance of singular point contact.

In another embodiment of the invention, the component has one or moreadditional sockets or projections located in a surface facing radiallyinward and engaging with one or more corresponding projections orsockets on a second inwardly located helically wound component, therebyto locate the inner winding with respect to the outer winding andtransmit radial forces, and resist relative axial sliding forces betweenthe windings, whilst allowing some rotation of the inner winding withrespect to the outer winding. Thus, the two components cooperate witheach other to minimise the stress experienced by each individualcomponent.

Preferably, the or each additional sockets or projections of the firstcomponent are positioned at a central location on the radially inwardlyfacing surface of the body. Thus, the stress at each of the radiallyinwardly facing edges is minimised.

Preferably, the helically wound inner component comprises a body havingcurved contours on two radially extending surfaces, such that adjacentturns of the winding co-operate with each other to remain substantiallytogether under conduit flexure.

Advantageously, the component forming the inner winding is characterisedby a cross-section whose second moment of area about the bi-normal(axial) direction is at least 20%,the second moment of area of the crosssection about the normal (radial) direction. Specifically, the componentforming the inner winding is characterised by a cross-section whosesecond moment of area about the bi-normal (axial) direction is at leasttwo thirds of, if not greater than, the second moment of area of thecross-section about the normal (radial) direction. Thus, the innerwinding is better capable to resist radial forces.

Preferably, the component forming the inner winding comprises one ormore fully enclosed internal cavities.

Preferably, the or each additional projection comprises one or more flatheaded portions connected to the body by linearly inclined edges.Preferably, the or each additional projection comprises one or more flatheaded portions connected to the body by curved surfaces. Conveniently,the or each additional projection may be rectangular in shape.Alternatively, the or each additional projection may be semicircular inshape.

Preferably, the or each additional projections comprises an enlargedhead portion connected to the body by a narrow neck portion, and the oreach additional sockets has an enlarged portion to receive the headportion of the projections and a narrow opening on which the neckengages to hold the projections captive in the sockets, the additionalsockets and projections having dimensions to allow a limited relativerotation between the adjacent inner and outer windings and to resistseparation, closing, and relative radial movement of the respectivewindings.

Preferably, the reinforced wall structure of the conduit comprises atleast one tubular braid located to provide additional axial tensilecapacity to the conduit. Preferably, the tubular braid is manufacturedfrom polymeric or textile materials including Kevlar™ fibres.

Advantageously, one or more of the helically wound components may bemanufactured from ferrous metals, including stainless steels.Preferably, one or more of the helically wound components aremanufactured from high strength steels.

Alternatively, the helically wound components may be manufactured fromnon-ferrous metals. Specifically, the helically wound components may bemanufactured from aluminum and its alloys. Alternatively, the helicallywound components may be manufactured from non-metallic materials.Alternatively, the helically wound components may be manufactured fromcomposite materials.

Preferably, one or more of the helically wound components may be appliedwith heat treatments to improve mechanical properties prior toconstruction of the conduit.

Advantageously, a polymeric or elastomeric sealing layer is located onone or more surfaces substantially circumferential to the axis ofsymmetry of the flexible tubular conduit.

Advantageously, the projections and/or sockets are coated with alubricating material. Specifically, the projections and/or sockets maybe coated with a lubricating material, such as oils, waxes, greases orgraphite.

Preferably, the projections and/or sockets contain one or more surfacerecesses. Conveniently, specifically shaped strips may be inserted intothese surface recesses, or onto the surfaces of projections or sockets.

Preferably, the projections and/or sockets are coated with a sealingmaterial, such as heavy hydrocarbons, including bitumen.

Preferably, the projections and/or sockets are coated with a polymericmaterial for the purposes of lubrication and/or sealing. Preferably, theprojections and/or sockets are coated with a polymeric material, such asglass filled P.T.F.E, for the purposes of lubrication and/or sealing.

Preferably, the projections and/or sockets are coated with a elastomericmaterial, such as polychloroprene, commonly known as Neoprene, for thepurposes of sealing.

In a further embodiment, each turn of the component is connected to anadjacent turn using a method of continuously linking the turns, by usingthe steps of applying pressure in a direction so as to force theprojections into the adjacent sockets, followed by pressure in a fartherdirection to substantially close the sockets onto the projectionsresulting in plastic deformation of at least the region around thesocket, and providing compressive stresses in the component. Preferably,heated rollers are used to apply pressure.

A particular advantage of the invention is that, unlike existingtechnology, the locking mechanism located in the axial direction givesthe flexibility to change area distributions of the profiled elements,and thus is not reliant upon scaling a profile up or down.

The invention will now be described in detail, by way of example only,with reference to the accompanying drawings in which:

FIGS. 1A to 1E is a schematic illustration of several examples offlexible pipe utilisation;

FIG. 2 shows a sectional representation of a prior art flexible pipe;

FIGS. 3A to 3D show a variety of existing profiles for the armour layers3 of FIG. 2;

FIG. 4 illustrates the normal, bi-normal and tangential axes withrespect to the axis of symmetry of a pipe;

FIG. 5 shows the orientation of “C-shape” armour profiles with respectto the axis of symmetry of the pipe.

The following figures shows various embodiments of the present inventionin which X—X represents the orientation of the axis of symmetry of theflexible tubular conduit:

FIG. 6 shows a helically wound component in which a cut has been made ina vertical plane of the winding;

FIG. 7 shows, in detail, the cross-sectional profile of the component ofFIG. 6;

FIG. 8 shows a further embodiment of the component of FIG. 7;

FIG. 9 shows a component cross-sectional profile in which the componentis an outer winding capable of engaging with the inner winding of FIG.11;

FIG. 10 shows a component projection in detail, and illustrates that thevarious forces are de-coupled and act at different locations;

FIG. 11 shows several component cross-sectional profiles in which thecomponent is an inner winding capable of engaging with the outer windingof FIG. 9;

FIG. 12 shows some possible variations in the component cross-sectionalprofile of the inner winding of FIG. 11;

FIG. 13 shows, in cross-section, an inner and outer winding in theengaged position. Fully enclosed internal cavities are also shown;

FIG. 14 shows a component projection in detail coated by a sealing orlubricating layer;

FIG. 15 shows a reinforcing tubular braid which may be applied to one ormore surfaces of the flexible tubular conduit.

FIGS. 16-18 illustrate a method of assembling the windings.

As described above, FIGS. 1-5 illustrate examples of the prior art and,as discussed previously, current practice uses either one or twosuperimposed layers of internal pressure armour (layers 3 and 4 of FIG.2 i.e. referred to as inner and outer windings respectively). Both ofthese configurations have been considered using the present invention.Generally, in the following discussion, the situation where the singlearmour layer 3 is used will be described (FIGS. 6-8) in detail prior todescribing the embodiments in which the two pressure armours 3 and 4 areused (FIGS. 9, 11 and 12). The present invention is also suitable foruse as the carcass layer 1.

FIGS. 6-8 show representations of the component 10 which are used tomake up layer pressure armour layer 3 when the optional layer of 4 isnot used FIG. 2). Although the component 20, shown in FIG. 9, ispreferably designed to engage with an inner winding 21, the component 20could also be used in situations without an engaging inner winding 21.The outline of the components 10 or 20 can be roughly square (FIG. 7),or can be even more rectangular (FIG. 9) with the shorter sides parallelto the pipe axis of symmetry X—X.

The mechanism used to connect subsequent turns of a winding is the samefor the situations in which a single winding is used, and also when bothan inner 3 and outer 4 winding are used. The mechanism to connect thesesubsequent turns consists of a projection 8 which mates with a socket 9in the next component turn. As shown in FIG. 8, more than one projectionand corresponding socket can be used. Each projection has an enlargedhead portion 11 connected to the body of component 10 by a narrow neckportion 12, and each socket has an enlarged portion 13 to receive thehead portion 11 of the corresponding projection and a narrow opening 14on which the neck 12 engages to hold the projection captive in thesocket. The projections 8 and sockets 9 are dimensioned to allow alimited relative rotation between the adjacent turns of the winding andto resist separation, closing and relative radial movement of therespective turns. There are many possible variations in the design ofthe axial projection 8 and socket 9 arrangement but several criticalfunctions, which are discussed below, will be enabled.

The effect of flexure on the conduit body is to produce local areas oftension and compression. An axial tension due to self weight will besuperimposed on this. It may occur that in some applications, such asdeep water, the pipe will see an axial compressive load. The primaryfunction of the axial projection 8 and socket 9 locking mechanism is toresist local axial loading due to flexure, and so a component with thislocking mechanism may have a substantial global tensile capacity. Thegeometry may be designed such that this capacity may be sufficient tosupport the self-weight of the pipe. This is enabled by designing theshape to have nearly vertical (radial) edges, as shown in FIG. 10 as A,which are optimal for resisting axial tension.

Similarly the almost vertical face, shown in FIG. 10 as B, is optimisedto resist compression of the layer (as will occur in flexure). Thetransmission of radial contact pressure through the mechanism will occuralong the areas shown as C in FIG. 10. This figure demonstrates twodistinctive features of the invention. The contact pressure istransmitted over a finite area, regardless of the degree of flexure.Furthermore, the effects of the primary and secondary loading modes,that is internal pressure and flexure, are de-coupled. Therefore, theydo not reach their maximum values at the same location, as was the casewith previous profiles. In addition, it can be seen that the socketrecess is reinforced by sufficient surrounding material to resist radialopening of the recess.

Ordinarily, the helically wound components are manufactured from ferrousmetals, including stainless steels. The above mentioned feature of theinvention may enable the safe use of higher strength steels (as anexample, those with an Ultimate Tensile Strength greater than 800 MPa)in, for example the offshore recovery applications discussed earlier, asconcerns about fatigue and fretting would be diminished.

By definition, a given force applied over a small area produces a higherpressure than the same force applied over a larger area. Thus, althoughin certain cases axial compression forces may be transmitted through thearea B of FIG. 10, the preferred arrangement is such that the axialcompression forces between adjacent turns of the winding aresubstantially transmitted through contact between radial sides of thecomponent body, and not through contact between projection and socket.Accordingly, the length of the projection measured from its root, on oneradial side of the body, is substantially shorter than the depth of thecorresponding socket, measured from the opposing radial side of thebody.

The capacity of the component to support high stress situations ispartially dependent upon the relative area distributions of the elementswhich make up the component, and increases as the relative area definedby the projection is reduced. By definition, the cross sectional areaencompassed by the component body excludes the area enclosed as thesockets, and any additional surface recesses (see later), but includesthe area defined by the projections and also any fully enclosed internalcavities (see later). Therefore, as can be seen in FIGS. 7 and 9, thecross sectional area of each projection is substantially less than thecross sectional area of the component body excluding the area of eachprojection. Preferably, the cross sectional area of each projectionshould be less than 50% of the cross sectional area of the componentbody excluding the area of each projection, but in particular less than30%.

By locating the projection 8 and socket 9 near the top of the component10 or 20, and radially away from the axis of symmetry X—X of theflexible tubular conduit (FIGS. 7 and 9), the projections 8 and sockets9 are located away from the areas of high stress. This also has theeffect of reducing the gap between turns at the top of the component 10or 20, which enables the use of a polymeric sealing layer on the outersurface of the component to seal against external pressure, andinherently reduces the load on the carcass layer 1. Thus, this may leadto a design of the flexible tubular conduit where no carcass 1 isrequired. Furthermore, this design should substantially increase theoperating depth of flexible pipes offshore by reducing the weight perunit length ratio of the pipe and also enabling a much higherhydrostatic pressure to be carried.

The use of a locking mechanism formed by projection 8 and socket 9located in the axial direction, gives the flexibility to change areadistributions of the helically wound component, and thus is not reliantupon scaling a profile up or down. For a given load case, the pressurecapacity of a layer, and thus the pipe, can be optimised by a userdefined area distribution and not one reliant upon scaling a givenprofile up or down. As an example, for a very high pressure capacity,the component could be designed so as to have a second moment of areagreater about the bi-normal axis (axial direction) than about the normalaxis (radial direction), this difference being represented by FIGS. 7and 9 where, by such an arrangement, the profile of the component shownin FIG. 9 has an inherently higher pressure capacity than that of theprofile of the component shown in FIG. 7. This relative areadistribution is also suitable for the inner winding 21.

The change in shape has the desirable effect of making thecross-sectional second moment of area about the bi-normal axis at leasttwo thirds of, if not greater than, the second moment of area about thenormal axis. These components may also be used as a carcass layer linside the polymer sealing layer 2. This would substantially improve thecollapse resistance of a flexible pipe by virtue of a controllable crosssectional flexural stiffness product of material Young's modulus andsecond moment of area). Furthermore, the lower stress regime incurred bythese profiles increases the plastic collapse pressure of the layer,which in turn reduces the likelihood of failure.

If two layers of pressure armour are utilised (i.e. layers 3 and 4 ofFIG. 2), the inner armour 3 profile may be adapted to minimise the gapsoccurring between successive turns of armour. In this case, the profileof the component of the present invention for use as layer 3, isdifferent from that described previously and consists of matching curvesapplied to the vertical faces (i.e. in the radial direction) of theprofile, as illustrated by the mating faces 15 of the components shownFIG. 11. This enables the component to move with pipe flexure whileminimising the aforementioned gap between turns of component.

An additional engaging arrangement comprising a projection 16 extendingfrom the inner component 21 (FIG. 12), to engage in a recess or socket17 located in the outer layer component 20, may be utilised (FIG. 13).Although the projection 16 is shown to emanate from component 21, theprojection 16 could emanate from component 20 and engage with acorresponding socket 17 in the component 21. Some variations on theshape of the projection 16 are shown in FIG. 12, and it is clear that itmay be rectangular (B), semi-circular (E) or hybrid (A, C, D, F) inshape. In addition, these engaging mechanisms are located centrally onthe surfaces of the components so as to minimise the stress at theedges.

The additional socket 17 has a corresponding shape such that theseadjacent components are allowed limited relative rotation and yet resistclosing and relative radial movement. As an example, the projection 16may comprise one or more flat head portions, which would avoid singularpoint contact, connected to the body of component 21 by inclined edges,which may be linear (FIG. 12, C) or curved (FIG. 12, F) or combinationsof both (FIG. 12, A). Alternatively, the projection may comprise anenlarged head portion connected to the body of component 21 by a narrowneck portion (FIG. 12, D) and be dimensioned such that when engaged withthe additional socket 17 of component 20, these adjacent components 20and 21 are allowed limited relative rotation and yet resist separation,closing and relative radial movement.

The projection 16 will not only act to transfer radial contact pressurebut also axial tension between the armour layers 20 and 21. As a resultof flexural loading, the projection 16 must allow some rotation of thelower component 21 with respect to the upper component 20 but this hasnot been found to be severe, mainly due to the flexural limitationsimposed by the polymeric layers in the pressure vessel structure.

As shown in FIG. 13, the connection mechanism 8 and 9 should be made inthe upper layer (component 20). This ensures that the stressconcentration, which is inevitable at the connection, acts in a regionof lower mean stress than would otherwise be the case. FIG. 13 alsoshows fully enclosed internal cavities 25 which may be used, in one ormore of the components, to reduce the weight of the pipe withoutsubstantially affecting the stress capacity.

It would be appreciated that many modifications to the above describedembodiments of the invention may be made by someone skilled in the art,without departing from the scope of the invention. Furthermore, aversion with a socket and/or projection (FIG. 14) coated with a material26 to provide a sealing or lubricating layer would be a usefulmodification. A tubular braid 50 (FIG. 15) may also be applied to one ormore windings to increase the axial tensile capacity of the pipe.

Other embodiments of the invention include the manufacture of thecomponents from non-ferrous metals such as aluminum and its alloys, ornonmetallic materials including composite materials. In addition, theprojection and socket mechanism may be coated with a lubricatingmaterial such as oils, waxes, greases or graphite. The projection andsocket mechanism may also be coated with a sealing material, such asheavy hydrocarbons, including bitumen. Moreover, a polymeric (such asglass filled P.T.F.E) or elastomeric layer (such as polychloroprene,commonly known as Neoprene) may be applied to aid lubrication and/orsealing. The projections and/or sockets may also contain one or moresurface recesses. Thus, the lubricating/sealing function can also beenabled by using specifically shaped strips which may be inserted intothe surface recesses, or onto the surfaces of projection or socket.These modifications are equally suitable to all connection or engagingmechanisms of both inner and outer windings.

The method of mating subsequent turns of the component may be carriedout using a press fit for steel components, as shown schematically inFIG. 16. Pressure is applied in the axial direction, by one or morerollers attached to the winding spindle, so as to force the projection 8into its corresponding socket 9 in a continuous manner. Alternativelythe strip may be manufactured with an open socket which is pressed shutduring assembly, causing plastic deformation of at least the surroundingarea (FIGS. 17 and 18). Compressive stresses would also be introducedwhich would increase the pressure capacity of the pipe.

The apparatus for constructing the present invention may be convenientlyretrofitted to existing equipment used in the winding process. Two orpreferably four diametrically opposite rollers would be used and thesemay be heated. In addition, heat treatments may be applied to theconduit to improve its mechanical properties.

In summary, unlike existing technology for helically wound reinforcementlayers for flexible tubular conduits, this invention provides a lockingmechanism located in the axial direction of the tubular conduit and thusgives the flexibility to change area distributions of the profiledcomponents, and improve the mechanical performance of the tubularconduit without being reliant upon scaling a profiled component up ordown.

In addition, the contact pressure is transmitted over a finite area,regardless of the degree of flexure of the tubular conduit. Furthermore,the loads due to internal pressure and flexure act at different pointsalong the locking mechanism and thus do not reach their maximum value atthe same location. Thus, the possibility of fatigue fracture andfretting is diminished, and the use of high strength steels is moreattractive.

This invention also provides an arrangement which reduces the gaps whichoccur between engaging faces of a helically wound component, and thusincreases the integrity of flexible tubular conduits. This is done byprofiling the radial edges of the components such that theysubstantially mate even when the conduit is under flexure. Furthermore,this invention provides inner and outer windings which engage with oneanother and thus co-operate to reduce the effective maximum stress seenby either windings.

What is claimed is:
 1. A flexible tubular conduit with a main conduitaxis and having a reinforced wall structure comprising at least onecomponent wound helically, the component comprising a body having one ormore projections extending axially from one or both body sides and acorresponding number of sockets on the opposing body sides, theprojections of one turn of the winding engaging in the sockets of thenext turn of the winding, each projection having an enlarged headportion connected to the body by a narrow neck portion, and each sockethaving an enlarged portion to receive the head portion of thecorresponding projection and a narrow opening on which the neck engagesto hold the projection captive in the socket, the sockets andprojections having dimensions to allow a limited relative rotationbetween the adjacent turns of the winding and to resist separation,closing, and relative radial movement of the respective turns, whereinthe tubular conduit is configured to operate at pressures of greaterthan 50×10⁵ N/m².
 2. A flexible tubular conduit as claimed in claim 1,wherein the cross sectional area of each projection is substantiallyless than the cross sectional area of the component body excluding thearea of each projection.
 3. A flexible tubular conduit as claimed inclaim 2, wherein the cross sectional area of each projection is lessthan 30% of the cross sectional area of the component body excluding thearea of each projection.
 4. A flexible tubular conduit as claimed inclaim 2, wherein the cross sectional area of each projection is lessthan 20% of the cross sectional area of the component body excluding thearea of each projection.
 5. A flexible tubular conduit as claimed inclaim 2, wherein the cross sectional area of each projection is lessthan 10% of the cross sectional area of the component body excluding thearea of each projection.
 6. A flexible tubular conduit as claimed inclaim 1, wherein axial compression forces between adjacent turns of thewinding are substantially transmitted through contact between radialsides of the component body and not through contact between projectionand socket.
 7. A flexible tubular conduit as claimed in claim 6, whereinthe length of the projection, measured from its root on one radial sideof the body, is substantially shorter than the depth of thecorresponding socket, measured from the opposing radial side of thebody.
 8. A flexible tubular conduit as claimed in claim 1, wherein thesocket recess is configured to resist radial opening of the recess.
 9. Aflexible tubular conduit as claimed in claim 8, wherein the socketrecess is reinforced by sufficient surrounding material to resist radialopening of the recess.
 10. A flexible tubular conduit as claimed inclaim 1, wherein the tubular conduit is configured to operate atpressures of greater than 100×10⁵ N/^(m2).
 11. A flexible tubularconduit as claimed in claim 1, wherein the tubular conduit is configuredto operate at pressures of greater than 200×10⁵ N/m².
 12. A flexibletubular conduit as claimed in claim 1, wherein at least one projectionand corresponding socket of the component are located at a positioncloser to the radially outer surface of the component than the radiallyinner surface.
 13. A flexible tubular conduit as claimed in claim 1,wherein the component is characterised by a cross section whose secondmoment of area about the bi-normal (axial) direction is at least 20% ofthe second moment of area of the cross section about the normal (radial)direction.
 14. A flexible tubular conduit as claimed in claim 1, whereinthe component is characterised by a cross section whose second moment ofarea about the bi-normal (axial) direction is at least two thirds of, ifnot greater than, the second moment of area of the cross section aboutthe normal (radial) direction.
 15. A flexible tubular conduit as claimedin claim 1, wherein the component has one or more additional sockets orprojections located in a surface facing radially inward and engagingwith one or more corresponding projections or sockets on a secondinwardly located helically wound component, thereby to locate the innerwinding with respect to the outer winding and transmit radial forces,and resist relative axial sliding forces between the windings, whilstallowing some rotation of the inner winding with respect to the outerwinding.
 16. A flexible tubular conduit as claimed in claim 15, whereinthe or each additional projections comprises an enlarged head portionconnected to the body by a narrow neck portion, and the or eachadditional sockets has an enlarged portion to receive the head portionof the projections and a narrow opening on which the neck engages tohold the projections captive in the sockets, the additional sockets andprojections having dimensions to allow a limited relative rotationbetween the adjacent second inner and first outer windings and to resistseparation, closing, and relative radial movement of the respectivewindings.
 17. A flexible tubular conduit as claimed in claim 1 whereinthe projections and/or sockets are coated with a polymeric material,from a list including glass filled P.T.F.E, for the purposes oflubrication and/or sealing.
 18. A method for constructing a flexibletubular conduit of the type claimed in claim 1, wherein each turn of thecomponent is connected to an adjacent turn using a method ofcontinuously linking the turns, by using the steps of applying pressurein a direction so as to force the projections into the adjacent sockets,followed by pressure in a further direction to substantially close thesockets onto the projections resulting in plastic deformation of atleast the region around the socket, and providing compressive stressesin the component.
 19. A method for constructing a flexible tubularconduit of the type claimed in claim wherein heated rollers are used toapply pressure.